This invention relates to the field of selectively addressable miniature battery-powered devices and, more particularly, to the provision of a power saving arrangement for such devices which also increases channel efficiency. Many schemes have been proposed for the conservation of power in small devices such as personal pagers which must be capable of receiving a signal, then detecting in that signal the address code of the pager and alerting the user. A device such as a pager must, obviously, be turned on continuously or for long periods of time. Battery drain is, therefore, a major consideration in circuit design.
The present system may be used with an address code detection system which is disclosed in U.S. Pat. Nos. 3,801,956 and 3,855,576, assigned to the same assignee as is the present invention, and which are incorporated herein by reference.
In the system of the above-referenced patents, a first address word is detected asynchronously and that detection provides automatic synchronization for a second word detect. Also included in that system is the capability of recognizing four function codes transmitted via the four combinations of the two words and their inverses. Battery-saving schemes in the prior art usually transmitted a turn-on code to the receiving unit and the unit was then turned off by an internal timer. One problem with such systems arises from the fact that, if a unit is in a low signal area when the turn-on code is transmitted, it would stay powered-down indefinitely.